Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted to a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in length). In addition, the wind turbines are typically mounted on towers that are at least 60 meters in height. Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators that may be rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid.
Wind turbine blades have continually increased in size in order to increase energy capture. However, as blades have increased in size, it has become increasingly more difficult to control optimum energy capture. As wind turbine blades grow larger, they undergo an increased aero-elastic response including deflection and twist when loaded that can negatively impact the energy capture. Additionally, turbine blades may be designed to have an aero-elastic response, with the twist of the blade dependent on the loading upon the blade. The blade loading is dependent on the wind speed, tip speed ratio (TSR) and/or pitch setting of the blade. TSR is the ratio of the rotational velocity of the blade tip to wind speed. It is important to optimize the operation of the wind turbine, including blade energy capture, to reduce the cost of the energy produced.
Therefore, what is needed is a method for operating a wind turbine that optimizes energy capture by controlling the TSR and blade pitch angle for the current operating condition.